Generally, a container refers to an object having a large box shape made of steel plates, and mainly used in freight transportation. Such a container not only stores and carries freight easily, but also has an advantage of protecting the freight contained inside it, and is thus being widely used.
Such a container is either transferred by the piece by means of a big freight vehicle that is used exclusively, or in large volumes by means of an exclusive train or exclusive ship.
Since such a container is made of steel material, it will occupy the same amount of space regardless of whether it is loaded with freight or it is empty. Therefore, there is a problem that the volume and cost for storing or transferring an empty container are the same as those for carrying freight inside the container.
In order to solve this problem, there have been attempts to enable a container to be folded when it is in an empty state, thereby solving the aforementioned problem. That is, Korean Patent Registration no. 10-1064803 discloses adopting a belt and a rotation axis rod in order to fold a container in an empty state, and a structure where the belt is fixed to a side wall of the container so that the side wall can be folded by pulling the rotation axis rod.
However, to fold the container, the aforementioned conventional technology requires additional components to be mounted, i.e. the rotation axis rod and the belt, and there is a safety problem that the side wall may be suddenly folded by the belt being pulled, and also a problem of difficulty in folding the door instead of the side wall, etc.
Meanwhile, there is a conventional technology, Korean Patent Registration no. 10-0775446, that discloses a foldable container, having a ratchet gear at a lower side plate of a left and a right plate 300, so that the container may be folded and unfolded simply and conveniently.
However, in the aforementioned conventional technology, in the process of folding an upper side plate and a lower side plate which form the left and the right plate, a front plate and a rear plate must be rotated towards the inner side of the container, in which case, a serious safety problem may occur, if there is a worker inside the container performing the operation of folding the container. That is, if the side wall is folded in the process of folding the front plate in order to fold the front plate towards the inner side of the container, a serious accident may occur.
Especially, since a plurality of containers are supposed to be stacked in a vertical direction to be stored and transferred, if the side wall cannot sufficiently support load being applied in the vertical direction, there is a concern that not only the contents may be damaged but also the plurality of stacked containers may collapse. However, the aforementioned conventional type of foldable container has a structure where the upper plate and the lower plate closely contact each other as the side wall is folded, and thus the container becomes very vulnerable to the stacked load acting in the vertical direction, thereby causing a problem of not being able to stack a sufficient amount of containers. Further, since it uses a method where the upper plate and the lower plate closely contact each other as the side wall is being folded, if the side walls at both sides are arbitrarily folded by the vertical load, a big accident may occur.